Empty nests in the great tit (Parus major) and the pied flycatcher (Ficedula hypoleuca) in a polluted area

Great tits (Parus major) are sometimes found to incubate in their nests eve n though the nests contain no eggs. This phenomenon has been observed in di fferent parts of Europe (Sweden, Finland, UK, Netherlands, Germany) and it has become more common during the 1980s. We analysed the occurrence of empt y nests in P. major and in pied flycatcher (Ficedula hypoleuca) in SW Finla nd from 6-year data collected in a polluted area around a copper smelter wh ich emits large quantities of sulphuric oxides and heavy metals. Among firs t broods 3.3% of P. major females incubated in empty nests. Incubation on e mpty nests was not observed in F. hypoleuca, but in this species 2.4% of th e nests remained without eggs. In both species empty nests were more common close to the pollution source than farther away. Histopathological analyse s in P. major suggest that there are diverse reasons for the incapability o f a female to lay. One out of five P. major females captured from incubatin g in an empty nest, had dark cysts in her oviduct. Two P. major females had very scanty medullary bone tissue in their tibiotarsus and tarsometatarsus and one female showed exceptionally high concentrations of lead in her bon e tissue. We conclude that air pollutants enhance the number of empty nests especially in F. hypoleuca, but cannot wholly explain the phenomenon in P. major. (C) 2000 Elsevier Science Ltd. All rights reserved.